1. Field of the Invention
This invention relates to compositions of ethylenechlorotrifluoroethylene polymers which are heat stabilized and which exhibit reduced metal corrosion.
2. Description of the Prior Art
Polymers of from about 40 to 60 mol percent ethylene, about 60 to 40 mol percent chlorotrifluoroethylene and optionally about 0.1 to 10 mol percent of 3,3,3-trifluoro-2-trifluoromethyl propene, certain vinyl monomers and mixtures thereof exhibit outstanding mechanical, electrical and chemical properties. In order to stabilize ethylene-chlorotrifluoroethylene copolymers against degradation and use at elevated temperatures, it has been suggested in U.S. Pat. No. 3,745,145 to Khattab et al. to incorporate a stabilizing system comprising (a) a phosphite of an organic polyhydric phenol, (b) a salt of a carboxylic acid and a metal of Group II of the Periodic Table and (c) a thio dipropionic acid ester or alkali metal salt. It has been further proposed in U.S. Pat. No. 3,773,698 to Khattab to further incorporate into such stabilizing system an alkaline earth metal oxide.
Although it has been found that the above-described stabilizing systems provide excellent resistance to degradation during melt processing as well as in many end-use applications, it has been discovered that some degradation occurs when wire and cable constructions provided with a coating of the copolymer are heated at elevated temperatures for considerable periods of time. Such problem is especially recognized in silver-plated copper wire constructions which are subjected to such thermal environments as 205.degree. C for three days. When the fluoropolymer coating is removed from the construction for splicing, soldering or other purposes, a red corrosion product is present on the surface of the silver plating. Such corrosion product may adversely affect electrical properties in some applications and may also prevent good electrical contact when soldered connections are made.
It would be desirable if there were provided a stabilizer system for such polymers which reduced metal corrosion, especially in wire and cable applications, without discoloring the resin when subjected to elevated temperatures. Typically, the fluoropolymer coating is color-coded for facilitating connections and thus it is important to retain the color-coding integrity of the coating.